Boreholes may be drilled into the ground for many different purposes. One purpose of drilling boreholes is to obtain core samples of the ground through which the drilling is being performed. It may be desirable to obtain core samples in connection with endeavours such as mineral exploration, scientific research, or geotechnical site investigations.
Core drilling for the purpose of obtaining core samples may be performed using a core drill which is located at the lower end of a drill string. The drill string is typically assembled from a plurality of drill rods which are connected together with threaded connections. The lowermost drill rod is known as a core barrel and is comprised of an outer core barrel and an inner core barrel which is secured within the outer core barrel at a drilling position. The core drill is connected with the core barrel and includes an annular cutting surface. The inner core barrel collects a cylindrical core sample from within the annular cut which is made by the annular cutting surface of the core drill. The inner core barrel contains and protects the core sample.
Following the collection of a core sample during core drilling, the inner core barrel must be removed from the interior of the drill string in order to extract the core sample from the inner core barrel, and a replacement inner core barrel must be inserted into the interior of the drill string and secured at the drilling position in order to enable a further core sample to be collected as drilling continues.
In conventional core drilling, the inner core barrel is removed from the interior of the drill string and the replacement inner core barrel is inserted into the interior of the drill string by first removing the entire drill string from the borehole.
In wireline core drilling, the inner core barrel is removed from the interior of the drill string without removing the entire drill string from the borehole, by using an inner core barrel retrieval device such as an overshot which is attached to the end of a wireline. The inner core barrel retrieval device is inserted into the interior of the drill string and passed through the interior of the drill string on the end of the wireline until it attaches with the inner core barrel. The inner core barrel retrieval device and the inner core barrel are then removed from the interior of the drill string by retracting the wireline. The replacement inner core barrel is then inserted into the interior of the drill string and passed through the interior of the drill string until it is secured at the drilling position, either with the wireline or by pumping the replacement inner core barrel through the interior of the drill string with a chaser fluid.
This process of removing an inner core barrel from the interior of the drill string and inserting a replacement inner core barrel into the interior of the drill string may be repeated several times or many times during the drilling of the borehole. As a result, it is apparent that an advantage of wireline core drilling over conventional core drilling is that wireline core drilling does not require the removal of the entire drill string from the borehole each time that the inner core barrel must be removed and replaced.
In the performance of land based conventional or wireline core drilling, it is feasible to carry out core drilling with as few as one or two inner core barrels. If a single inner core barrel is used, drilling must be interrupted while the inner core barrel is removed from the interior of the drill string, while the core sample is extracted from the inner core barrel, and while the inner core barrel is reinserted into the interior of the drill string. If two inner core barrels are used, drilling must be interrupted while the first inner core barrel is removed from the interior of the drill string and while the second core barrel is inserted into the interior of the drill string, but the core sample may be extracted from the first inner core barrel while the second core barrel is being inserted into the interior of the drill string.
The performance of underwater conventional or wireline core drilling involves challenges which are not encountered in the performance of land based core drilling.
For example, underwater core drilling may be performed using drilling equipment which is deployed and controlled from a barge, ship or platform which is located on the surface of a body of water, or may be performed using remotely operable underwater drilling equipment which is operatively connected to a barge, ship or platform with only a deployment cable and/or a control cable.
An advantage of using remotely operable underwater drilling equipment for underwater core drilling is that the underwater equipment is not generally affected by movement of the barge, ship or platform which is located on the surface so that the stability of the underwater equipment is not dependent upon the stability of the surface equipment. As a result, the underwater equipment may typically be constructed to be relatively small and light.
A disadvantage of using remotely operable underwater drilling equipment for underwater core drilling is that although the operation of the underwater equipment may be controlled from a control location on the surface of the body of water, the entire drilling operation must typically be essentially self-contained and performed without physical interaction with the surface.
As one example, underwater drilling equipment must typically carry a supply of drill rods and inner core barrels which is sufficient to enable drilling to a desired depth and the collection of a desired number of core samples. Consequently, a storage area must typically be provided on the underwater drilling equipment for a number of drill rods and inner core barrels.
As a second example, the underwater drilling equipment must be capable of operating remotely without manual adjustment or repair since direct human intervention with the underwater drilling equipment is not typically possible when the equipment is deployed underwater.
As a result, the underwater drilling equipment and its operation are preferably made simple and robust so that an amount of reliability in the underwater environment can be achieved.
U.S. Pat. No. 7,380,614 (Williamson et al) describes a remotely operated water bottom based wireline drilling system and a wireline drilling method.
The wireline drilling system described in U.S. Pat. No. 7,380,614 (Williamson et al) includes a frame, a support structure movably coupled to the frame, a drill head mounted on the support structure, a winch including a cable coupled to the support structure, a latching device located on the end of the cable for latching onto a core barrel, a storage area associated with the frame for drill rods and core barrels, and at least one clamp associated with the frame and arranged to fix a vertical position of a drill string over a drill hole.
The wireline method described in U.S. Pat. No. 7,380,614 (Williamson et al) includes disposing the drilling system on the bottom of a body of water, drilling into a formation which is below the bottom of the body of water by rotating a first drill rod having a first core barrel latched therein and advancing the drill rod longitudinally, opening an upper end of a first drill rod by removing the drill head therefrom by displacing the drill head vertically and/or laterally relative to the upper end of the first drill rod, lowering the cable having the latching device into the first drill rod, retracting the cable to retrieve the first core barrel, laterally displacing the first core barrel from the first drill rod, inserting a second core barrel into the first drill rod and latching it therein, affixing a second drill rod to the upper end of the first drill rod; and resuming drilling the formation by longitudinally advancing and rotating the first and second drill rods. The above method steps may be repeated to include additional core barrels and additional drill rods as drilling progresses.
The wireline drilling system and wireline drilling method described in U.S. Pat. No. 7,380,614 (Williamson et al) do not facilitate or contemplate inserting and/or retrieving a core barrel from the interior of the drill string while the drill head is connected with the drill string.